Photonic integrated circuits are widely used in optical communication systems, in particular to implement optical transceivers. An optical transceiver may include an optical transmitter for transmitting optical signals into a fiber optic link, and an optical receiver for receiving optical signals from the fiber optical link. Often the optical link includes an optical amplifier, such as an erbium-doped fiber amplifier (EDFA) in the vicinity of the optical transceiver, which has to be optically pumped by pump light, which may propagate towards the transceiver or away from the transceiver. Typically an optical isolator is required either at the optical link side or at the transceiver side of the EDFA to filter out the pump light. This is illustrated by way of example in FIG. 1, which shows an optical transceiver 10 including an optical transmitter (Tx) 12 and optical receiver (Rx) 11, and two EDFAs 21 connecting them to an optical link 50. Pump lasers 23 generate pump light, which is then fed into each EDFA 21 through a wavelength division multiplexing (WDM) coupler 31 for optically pumping the respecting EDFAs 21 in a counter-propagating fashion. Optical isolators 41 are included in each of the Rx and Tx paths to prevent the pump light from entering either the optical link 50 or the transceiver PIC. Although pumping an EDFA 21 in the direction of the transceiver allows to eliminate an optical isolator at the optical link side of the EDFA, the pump light entering a semiconductor layer of a PIC implementing the transceiver may be absorbed in that layer, causing a reduction in the optical power of signal light through free carrier absorption.
This general scheme, although capable of performing its function, requires however a relatively large number of optical components, which increases its cost and size.